Geopolymers

Structures, Processing, Properties and Industrial Applications

J L Provis, J S J van Deventer

• Publisher: Woodhead Publishing
• Year: 2009
• Print ISBN: 9781845694494
• eBook ISBN: 9781845696382
• Topic: Technology & Engineering
• Subtopic: Environmental Management
• Index: Technology & Engineering

A geopolymer is a solid aluminosilicate material usually formed by alkali hydroxide or alkali silicate activation of a solid precursor such as coal fly ash, calcined clay and/or metallurgical slag. Today the primary application of geopolymer technology is in the development of reduced-CO2 construction materials as an alternative to Portland-based cements. Geopolymers: structure, processing, properties and industrial applications reviews the latest research on and applications of these highly important materials.Part one discusses the synthesis and characterisation of geopolymers with chapters on topics such as fly ash chemistry and inorganic polymer cements, geopolymer precursor design, nanostructure/microstructure of metakaolin and fly ash geopolymers, and geopolymer synthesis kinetics. Part two reviews the manufacture and properties of geopolymers including accelerated ageing of geopolymers, chemical durability, engineering properties of geopolymer concrete, producing fire and heat-resistant geopolymers, utilisation of mining wastes and thermal properties of geopolymers. Part three covers applications of geopolymers with coverage of topics such as commercialisation of geopolymers for construction, as well as applications in waste management.With its distinguished editors and international team of contributors, Geopolymers: structure, processing, properties and industrial applications is a standard reference for scientists and engineers in industry and the academic sector, including practitioners in the cement and concrete industry as well as those involved in waste reduction and disposal. - Discusses the synthesis and characterisation of geopolymers with chapters covering fly ash chemistry and inorganic polymer cements - Assesses the application and commercialisation of geopolymers with particular focus on applications in waste management - Reviews the latest research on and applications of these highly important materials

1

Introduction to geopolymers

J.L. Provis; J.S.J. Van Deventer University of Melbourne, Australia

Abstract

This introductory chapter provides a brief overview of some important aspects of geopolymer technology, in particular its historical development and the terminology by which geopolymers are described. An introduction to geopolymer technology from a scientific viewpoint is also given. The scope of this review is confined to predominantly low-calcium materials, i.e. ‘traditional’ alkali-aluminosilicate geopolymers, to the exclusion of alkali-activated slags and other related materials.

Key words

geopolymer

inorganic polymer

aluminosilicate

alkali activation

1.1 History of geopolymer technology

The term ‘geopolymer’ was coined in the 1970s by the French scientist and engineer Prof. Joseph Davidovits, and applied to a class of solid materials synthesised by the reaction of an aluminosilicate powder with an alkaline solution (Davidovits 1982a, 1991, 2008). These materials were originally developed as a fire-resistant alternative to organic thermosetting polymers following a series of fires in Europe, and products based on this initial work have since found application as coatings for fire protection for cruise ships (Talling 2002), as a resin in high-temperature carbon-fibre composites (Lyon et al. 1997), in thermal protection of wooden structures (Giancaspro et al. 2006), as a heat-resistant adhesive (Bell et al. 2005, Krivenko and Kovalchuk 2007), as a monolithic refractory (Comrie and Kriven 2003, Kriven et al. 2004), and in various other niche applications. However, as can be seen from a brief perusal of the Table of Contents of this book, the primary application for geopolymer binders has since shifted to uses in construction. This is primarily due to the observation, first published by Wastiels et al. (1993), that it is possible to generate reliable, high-performance geopolymers by alkaline activation of fly ash, a by-product of coal combustion.

The synthesis of construction materials by alkaline activation of solid, non-Portland cement precursors (usually high-calcium metallurgical slags) was first demonstrated by Purdon (1940). Detailed lists of key historical references and milestones in the development of alkali-activated binders have been presented in various review papers (Malone et al. 1985, Krivenko 1994, Roy 1999, Krivenko 2002); the majority of these relate to the alkaline activation of blast furnace slags, and so are beyond the scope of the current discussion. A very extensive review focussed predominantly on alkali activation of metallurgical slags has recently been published (Shi et al. 2006), and the reader is referred to that excellent book for information in that area. The key distinction to be made here is that the alkaline activation of slags produces a fundamentally calcium silicate hydrate-based gel (Richardson et al. 1994, Wang and Scrivener 1995, Shi et al. 2006), with silicon present mainly in one-dimensional chains and some substitution of Al for Si and Mg for Ca, whereas the geopolymer gel is a three-dimensional alkali aluminosilicate framework structure (Duxson et al. 2007b). The role of calcium in geopolymers is a matter still under investigation; some of the subtleties of calcium chemistry in geopolymers will be discussed throughout this book.

Much of the early published research into aluminosilicate geopolymers was published in the patent literature (for example: Davidovits 1982b, 1984), and so contains little scientific detail. Probably the most valuable documents summarising work throughout the 1980s are the proceedings of a conference (Geopolymer ’88) held in France in 1988 (Davidovits and Orlinski 1988), and a review paper authored by Davidovits (1991). Shortly after this, Palomo and Glasser published the first detailed scientific study of metakaolin geopolymers (Palomo and Glasser 1992), followed shortly afterwards by an extremely valuable three-part series by Rahier et al. (1996a, 1996b, 1997). These papers laid the groundwork for both broader and deeper study of metakaolin geopolymers in the ensuing decade, in particular work by groups in Spain (Granizo and Blanco 1998, Palomo et al. 1999b, Alonso and Palomo 2001), New Zealand (Barbosa et al. 2000, Barbosa and MacKenzie 2003), Germany (Kaps and Buchwald 2002, Buchwald et al. 2003, Buchwald 2006), and Australia (Yip and van Deventer 2003, Duxson et al. 2005, Perera et al. 2005, Singh et al. 2005, Steveson and Sagoe-Crentsil 2005). The proceedings of Geopolymer conferences held in 1999 (Davidovits et al. 1999), 2002 (Lukey 2002) and 2005 (Davidovits 2005) also provide valuable information regarding both technical developments in the field and the worldwide growth in geopolymers research during this period. A book published recently by Davidovits (2008) also summarises a good deal of work that was only previously available in the patent literature.

Research into fly ash geopolymers has grown from the aforementioned conference paper by Wastiels et al. (1993) to now form the bulk of applications-oriented research in this field. Fly ash has long been used in Portland cement concretes to enhance flow and other properties (Diamond 1986, Bouzoubaâ et al. 1999, Manz 1999), to reduce the carbon footprint of concrete, as well as simply a means of disposing of some of the many millions of tonnes of fly ash produced worldwide each year. Additional early reports of geopolymerisation of ASTM Class F (low-calcium) fly ash were provided by a number of researchers (van Jaarsveld et al. 1997, 1998, Palomo et al. 1999a, van Jaarsveld 2000, Krivenko and Kovalchuk 2002, Lee and van Deventer 2002, Swanepoel and Strydom 2002, Fernández-Jiménez and Palomo 2003, Rostami and Brendley 2003, Hardjito et al. 2004, Palomo et al. 2004), along with a proliferation of patents. Possibly due to the inherent difficulty associated with detailed scientific analysis of highly heterogeneous fly ash-based geopolymers, the level of understanding of fly ash geopolymers currently appears to lag behind their metakaolin-based counterparts. Metakaolin geopolymers are often used as a ‘model system’ by which the more commercially relevant fly ash-based materials may be better understood (van Deventer et al. 2007), and the exact degree to which this relationship holds has been the subject of some recent scrutiny (Lloyd 2008).

It is also necessary to note that various theories have been proposed attempting to link aspects of geopolymerisation technology to the construction of ancient structures, most particularly the Pyramids of Egypt (Davidovits and Davidovits 2001, Barsoum et al. 2006). While the veracity of such arguments is still under quite intense debate in some circles, it is clear that whether or not the Pyramids were ‘poured’ as synthetic stone blocks, the chemistry involved in such an undertaking would have been some distance away from the alkali-activated aluminosilicate systems which today are described as geopolymers (Barsoum et al. 2006). However, it is not the role of this Introduction to attempt to speculate regarding such issues.

1.2 Geopolymer terminology

In the context of this book, a ‘geopolymer’ is in general defined as a solid and stable aluminosilicate material formed by alkali hydroxide or alkali silicate activation of a precursor that is usually (but not always) supplied as a solid powder. The same term has also been used to describe organic polymers formed under geological conditions (e.g., coal); in spite of some highly speculative discussions to the contrary (Davidovits 2008), these materials are entirely unrelated to aluminosilicate geopolymers and will not be discussed in detail here.

The materials referred to here as ‘geopolymers’ have also been described in the academic literature as ‘mineral polymers’, ‘inorganic polymers’, ‘inorganic polymer glasses’, ‘alkali-bonded ceramics’, ‘alkali ash material’, ‘soil cements’, ‘hydroceramics’, and a variety of other names. The major impact of this proliferation of different names for essentially the same material is that researchers who are not intimately familiar with the field will either become rapidly confused about which terms refer to which specific materials, or they will remain unaware of important research that does not appear upon conducting a simple keyword search on an academic search engine. A prime example of this is the very valuable early work of Rahier and colleagues (Rahier et al. 1996a, 1996b, 1997), who used the term ‘inorganic polymer glass’ rather than ‘geopolymer,’ and so these papers have received far fewer citations than their quality and importance deserve. The terms ‘geopolymer’ and ‘inorganic polymer’ are gaining increasing ubiquity in the academic research field, and will be used essentially interchangeably throughout this book. Geopolymers are a subset of the broader class of alkali-activated binders (Shi et al. 2006), which also includes materials formed by alkali-, silicate-, carbonate- or sulfate-activation of metallurgical slags and giving a product that is pr...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Contributor contact details
• 1: Introduction to geopolymers
• Part I: Geopolymer synthesis and characterisation
• Part II: Manufacture and properties of geopolymers
• Part III: Applications of geopolymers
• Index